The present invention relates to induction heating of metal products having a cross-sectional area which is relatively small as compared to their length.
Induction heating apparatuses have been provided in which metal products travel through successive inductor coils belonging to separate heaters and are supported by means, generally rollers, placed between the heaters. That approach is not satisfactory when the products are flat and of great width, such as blooms. Such products need be supported at locations whose longitudinal spacing is small and further decreases as the metal is heated to a higher temperature. The space available for the inductors between two successive supports is small and the space which would be taken up by the rollers, because of their number and their diameter, would increase excessively the length of the furnace.
In another prior art apparatus, the blooms are moved from one furnace to the next by trolleys provided with lifting fingers. The fingers support the blooms placed on edge. The trolley comes under a first furnace into which the fingers lift the bloom. Once the bloom has been heated, the fingers take it down again, the trolley moves under a second furnace into which the fingers introduce the bloom, and so on. Such a procedure has numerous disadvantages: it is not continuous; the blooms must be rotated by 90.degree. since they are delivered flat by the rolling mill; it does not use the whole of the possibilities offered by induction heating; handling is complex; the hot blooms travel in free air and their surface becomes oxidized; the apparatus is not practical for blooms of very great length or comprising edges which are not strictly flat and at right angles to the larger faces.
It is an object of the invention to provide an improved apparatus for induction heating of flat metal products of large size; it is a more particular object to provide an apparatus which is continuous in operation, avoids movement of the products in free air between two heating operations, accepts blooms of very great widths and allows the blooms to be supported at very close intervals, whereby they retain a favorable rectilinear shape.
In general, the invention contemplates an apparatus for heating flat long metal products such as flats, slabs and blooms, comprising means for supporting said products and advancing them along the tunnel, typically in the direction of the great length of the products, said products resting flat on said means on one of the larger surfaces thereof; electrical means for heating the products by induction which comprise at least two flat inductors (typically multiphase inductors creating a sliding field moving in the longitudinal direction of the tunnel) placed one above the path of travel of the product and one under that path. The supporting and advancing means will typically project through the lower inductor.
The inductors may be designed for varying the amount of heat delivered in the product as it moves along the path of travel. For example, it may be desirable to dissipate high power in the initial part of the furnace, in order to bring the product rapidly to a required temperature. In the downstream part, a lower power may be sufficient to maintain the temperature. It will be generally advantageous to split up the furnace, in the direction of its length, into several sections provided with separate temperature regulating means for possible adjustment of the powers in those fractions of the inductors which are located in the successive sections. The temperature rise curves may be adapted to the different grades of metal to be treated and create, if necessary, a final zone of homogenization. Access to the furnace can be retained through the lateral walls of the tunnel, since there are no electrical conductors at that location.
The support and advancing means may be so called "pilgrim step" conveyor supporting the products by means of fingers projecting through the lower inductor. These fingers are connected to a mechanism which is below the inductor located close to the product to be heated.
The supporting and advancing means may also be in the form of disks projecting through the lower inductor and fixed on shafts located outside the tunnel.